This invention relates to a bio-compatible, implantable stimulating electrode, of the bipolar type, for chronic use, on atrial or ventricular surfaces of the heart, in experimental studies. In another aspect, the invention relates to such an electrode for use in conscious animal studies.
More particularly, the invention relates to an electrode for use in an animal testing PES program (Programmed Electrical Stimulation Testing), for testing of antiarrhythmic drugs. The type of testing which is conducted with the device of the present invention closely correlates to the PES testing done on humans to ascertain which antiarrhythmic drug is useful for their particular condition.
In the human case, a patient who has had a myocardial infarct is at risk of having another. Such a patient is then usually directed to a catheterization lab where he is catheterized to the heart. Ventricular tachycardia or fibrillation is induced and then converted to normal rhythm, and the patient is then tested with drugs to ascertain which antiarrhythmic drug decreases or prevents the fibrillation from occurring. The device of the present invention is for use in carrying over this type of testing to animals to avoid having to conduct it on humans while still reliably determining which antiarrhythmic drugs will work on humans.
In the prior art a number of electrodes have been developed to permit this type of PES testing. However, all suffer the disadvantage that they either cause extensive heart tissue damage with use, or have proven unreliable. More particularly, such devices include bipolar plunge wires, acrylic plaques and vinyl plaques. These items either work their way free from securing sutures because they do not flex with the animal heart, or the wires break where they joined the electrode.
Since considerable time and effort is involved in the preparation and study of these animals, it is vital that the electrodes used be reliable in performance over long periods of time and not cause extensive damage to the heart tissue. Many of the studies are conducted weeks or months after the initial surgical installation of the stimulating electrodes and because of the dog's impaired condition (myocardial infarct), it would not be feasible to re-instrument the dog if the electrode needed replacement because of malfunction.
A specific prior art implantable electrode structure, U.S. Pat. No. 4,125,116, is constructed so that the stimulating electrode conducting portion is embedded in a foam silicon rubber cushioning material so that the electrode structure will adapt more readily to the irregularities in the tissue surface. This structure, while attempting to provide for a secure attachment due to its flexibility, still encounters problems in use as discussed above since it will tend to separate from the tissue.
Another prior art electrode is disclosed in U.S. Pat. No. 4,030,509. This patent teaches a defibrillating electrode made of a metallic mesh which is insulated at its exterior surface by a layer of silicone rubber insulation. The electrode wraps around the heart in a complicated arrangement. This device includes a number of disadvantages since it cannot be readily adapted for experimental animal studies. Moreover, the relatively large metallic mesh, when in use, will often cause significant scarring and ultimate destruction of the tissue with which it is in contact.
U.S. Pat. No. 4,355,642, teaches a bipolar electrode manufactured of a mesh of synthetic fibers affixed to a disc. The mesh serves the purpose of permitting tissue ingrowth in the main electrode body to enhance attachment. A central spike or helix is required to penetrate the tissue to insure complete attachment. The spike or helix penetration causes damage within and without the surrounding tissue of the heart. The spike and helix are manufactured from platinum-iridium wire; another like structure is taught in U.S. Pat. No. 4,010,758.